1. Field of the Invention
The present invention relates to an electron emitter which is suitably employed as an electron beam source in a variety of apparatuses that utilize electron beams, including a field emission display (FED), an electron beam irradiation apparatus, a light source, an electronic-component-manufacturing apparatus, and an electronic circuit component.
2. Description of the Related Art
Such an electron emitter includes an emitter section which is provided in a reduced-pressure atmosphere having a predetermined vacuum level. The emitter section is configured so that it can emit electrons into the reduced-pressure atmosphere through application of a predetermined driving electric field.
In an FED, a plurality of electron emitters having the aforementioned configuration are two-dimensionally arrayed on a substrate formed of, for example, glass or ceramic material. In addition, a plurality of phosphors corresponding to the electron emitters are arrayed with a predetermined gap provided therebetween by the aforementioned reduced-pressure atmosphere. The FED is configured so that electrons emitted from the electron emitters fly through the aforementioned gap and collide with the phosphors, and the phosphors hit by the electrons fluoresce, thereby displaying a desired image.
Known electron emitters having the aforementioned configuration include an electron emitter having an emitter section formed of a dielectric material (piezoelectric material). Such an electron emitter is called a “piezoelectric-film-type electron emitter.” This type of electron emitter is produced at low cost, and therefore is suitable for use in an FED, in which, as described above, numerous electron emitters are two-dimensionally arrayed on a substrate having a relatively large area.
A conventionally known piezoelectric-film-type electron emitter is disclosed in, for example, Japanese Patent Application Laid-Open (kokai) No. 2005-183361.
The aforementioned piezoelectric-film-type electron emitter includes an emitter section formed of a dielectric layer, a first electrode, and a second electrode. The first electrode is provided on the top surface of the dielectric layer. The second electrode is provided on the bottom surface of the dielectric layer. On the top surface side of the dielectric layer, a portion of the emitter section in the vicinity of the peripheral edge of the first electrode is exposed to the outside of the piezoelectric-film-type electron emitter (i.e., to the aforementioned reduced-pressure atmosphere). The piezoelectric-film-type electron emitter is configured so that the thus-exposed portion serves as an electron emission region, which plays an important role for electron emission in the electron emitter.
The piezoelectric-film-type electron emitter having the aforementioned configuration is operated as follows. Firstly, in the first stage, voltage is applied between the first electrode and the second electrode so that the first electrode is higher in electric potential. An electric field generated by the applied voltage brings the emitter section into a predetermined polarization state. Subsequently, in the second stage, voltage is applied between the first electrode and the second electrode so that the first electrode is lower in electric potential. Through this voltage application, the polarization of the emitter section is inverted, and electrons are accumulated on the electron emission region. Subsequently, in the third stage, voltage is again applied so that the first electrode is higher in electric potential. Through this voltage application, the polarization of the emitter section is re-inverted. With this polarization inversion, the electrons accumulated on the electron emission region are emitted from the emitter section by means of electrostatic repulsion between the electrons and dipoles, and the thus-emitted electrons fly in the aforementioned reduced-pressure atmosphere. Thus, the piezoelectric-film-type electron emitter emits electrons.
However, the aforementioned conventional piezoelectric-film-type electron emitter involves a problem in that electron emission quantity is considerably reduced with repeated use thereof. Among components of the piezoelectric-film-type electron emitter (i.e., the aforementioned emitter section, first electrode, and second electrode, and a substrate for supporting the emitter section and electrodes), the emitter section would generally undergo change in properties with repeated use of the electron emitter. Therefore, reduction in electron emission quantity is considered to be caused mainly by impairment of the emitter section with repeated use of the piezoelectric-film-type electron emitter.
Conceivably, impairment of the emitter section is due to deterioration of the electron accumulation ability thereof. Specifically, impairment of the emitter section is considered to occur through the following mechanism: reduction in the amount of electrons accumulated on the emitter section lowers the amount of electrons which fly in the aforementioned third stage, whereby electron emission quantity is reduced.
Conceivably, deterioration of the electron accumulation ability of the emitter section is caused mainly by deterioration of the electrical insulating properties of the surface of the emitter section. Conceivably, deterioration of the insulating property of the surface of the emitter section occurs as a result of precipitation of an elemental metal through reduction of a corresponding metal element contained in a dielectric material constituting the emitter section. Particularly, in a reduced-pressure atmosphere, such precipitation of elemental metal through reduction of the dielectric material is likely to occur, since oxygen partial pressure is low in the atmosphere.
The aforementioned piezoelectric-film-type electron emitter generally employs a lead-containing piezoelectric material as a dielectric material. When the piezoelectric-film-type electron emitter formed of such a lead-containing piezoelectric material is operated in a reduced-pressure atmosphere, metal lead tends to precipitate on the surface of the emitter section.